Him being a wanker and seeing someone else is not a real reason to stop him from seeing his kids. If he's abusive or a danger to the kids, yes, stop contact. But doing it cos it's new partner is barely legal isn't a good reason. Set some ground rules; wait till they've been in a relationship for a set period of time before she meets the kids, make sure you meet her first before the kids do, she's not allowed to come first when it comes to him having contact etc. Not letting him have contact will impact the kids.

Hes also a drug user and getin into fights alot hes always got black eyes. He was not stable with his contact before i stopped it but because of family history (he has a family member on sex offenders reg) im very uncomfortable with his relationship.

I do want them to see him i just dont want them growing up thinking its ok to groom someone as thats kind of what he did with this girl. I dont want my dd at 16 seeing a 26 year old or my ds at 26 seeing a 16 year old

She's over the age of consent so he hasn't groomed her. I became involved with a 27 year old when I was aged 17. I wasn't groomed - he was an immature idiot which is why someone younger suited him but the relationship didn't damage me. You sound more worried about his relationship than the drugs and fighting.